QuickDraw and chart feature request

[AnotherDad]

You know water levels vary regardless of whether you're on a lake or coastal area so depth is relative. Lakes may not vary as quickly, but some lakes change more quickly than others.

1. It would be nice if charts automatically adjusted contour depths based on current water levels. It could do that by taking current depth when crossing a known contour line and automatically applying an offset to the entire chart.

2. That ability would really come in handy when using QuickDraw. Syncing/meshing recordings of the same area from different trips would be a lot easier if it automatically applied an offset to the current recording based on a known datum point.

[TroyBoy30]

http://www8.garmin.com/contactUs/ideas/

[Larry3215]

That would only work in areas with fairly flat bottoms. Other wise, GPS errors could cause your lake level to vary constantly all day long as your GPS position shifted - even when the boat didnt move.

There are many places in lakes I fish where a change in position of 10 feet to one side or the other can change depth by 10 feet or sometimes much more.

[AnotherDad]

Troy, I submitted the idea to Garmin already. :) But I thought I'd share here as well to see what others thought.

Larry, GPS is good for 9' horizontal accuracy. So there's some error but you can smooth that out by averaging the offset over the last N readings. Let's say N=10, so each new reading will result in a small change to that average offset. That might bother some people but I think it's better than a chart taken when a lake is full that you're using when the lake is half empty.

[Larry3215]

I think thats going to be more difficult and cause more depth variation than you think. For starters, there is no way to know what the exact GPS error is when you first lay down a recording in QD. You could be off to the north, south, east or west. When you come back three days later any error will be different. Heck, 5 minutes later it will be different. You would need to sit in one spot quite a while to get a decent average. But - you would have to do the same on the initial recording or it would be useless trying to compare the two. Even then, there is no guarantee your two averages would be "close enough" to avoid major depth errors in a lake with significant depth contours.

The QD folks already have a solution - there is a built in offset to do what you want. You need to change it when you visit that lake to what ever the current water level offset happens to be depending on lake level. Its not automatic, but it is accurate if you know the lake levels.

[AnotherDad]

I think thats going to be more difficult and cause more depth variation than you think.

Based on my prior experience with GPS data loggers (autocross and hiking), I think the horizontal GPS error isn't as big a problem as you think--especially when averaged over N readings.

you would have to do the same on the initial recording or it would be useless trying to compare the two. Even then, there is no guarantee your two averages would be "close enough" to avoid major depth errors in a lake with significant depth contours.

The point is not to overwrite existing depth contours, but to mesh them together like a jigsaw puzzle. Let's say I have a built-in chart with 25' contours. I use QD to get 1' contours, but the actual depth doesn't match the built-in map. Hence the new feature to take today's QD data and "paste" it onto the existing chart to fill in the gaps as it were.

The QD folks already have a solution - there is a built in offset to do what you want. You need to change it when you visit that lake to what ever the current water level offset happens to be depending on lake level. Its not automatic, but it is accurate if you know the lake levels.

There's the rub. How do you know what the lake levels are? They may be posted but when was the measurement taken and how much has it changed since then?

Again, the key change is meshing each QD run to existing data so what you get today fills in the gaps of what you already have rather than completely overwriting it. I think that would be a great feature, but I'm also a newbie at all this so my perspective may be off. I have lots of software design experience but relatively little on-water experience.

[Larry3215]

Whether you are correct or not as far as how to fix it, you have pointed out the major flaw in QD and all the other auto mapping programs out there - how to deal with fluctuating water levels.

It will be interesting to see if Garmin does anything with your idea. As far as I know, no one else does what you are suggesting with their auto mapping programs.

The only way I could think of to achieve what you want when you dont have good lake level info is to do the following.

1) Pick a spot near where you launch that has a relatively flat bottom and also allows you to position the boat very accurately out on the water - preferably without relying 100% on GPS. However, if the bottom is really flat, then GPS is fine.
2) Make a note of the depth reading at that exact spot. Write it down because you're going to need it later.
3) Then start doing your QuickDraw recording as normal.
4) Here is the key part - next time you go to that lake, park the boat in the exact same spot and check the depth. If it has changed (you did write it down?), then change your depth offset in QD to adjust for the new water level.
5) Then start your new QD recording.

[AnotherDad]

Yeah, I think marking a baseline datum you start all QD mapping from is the only way to be sure. You may be off, but at least you'll be consistently off. In my area we're experiencing record drought and most lakes are reservoirs, so that datum has to be relatively deep. One place (New Melones lake) has gotten so low all three paved launch ramps are out of service and we're using a dirt ramp. https://www.google.com/maps/@37.9919.../data=!3m1!1e3

But applying a (temporary) global offset to water depth should be an easy feature to implement. If you look at that same google map, there are two "islands" just west of the launch ramps that normally are submerged. They aren't now and it would be nice to have them show on charts as land rather than under water.

[mosin]

Another way that i can think of is using the altitude reported by gps. To do that, youll probably need to use nmea recordings (avail in play store), record and average the reading for a period of time for a given spot. Offset that reading to account distance between receiver and water surface etc.. However, the best vertical gps reading could probably be a yard off. Thats my idea, especially thinking about lakes without official water level outside US.<br><br>Hopefully garmin will let us get the raw data from qucikdraw. Being open with the dàta will allow us to tinker with it and possibly improves it too. Their handheld gps units certainly benefitted a lot from user contributed 'open' data from openstreetmaps.

[skid00skid00]

Another way that i can think of is using the altitude reported by gps. To do that, youll probably need to use nmea recordings (avail in play store), record and average the reading for a period of time for a given spot. Offset that reading to account distance between receiver and water surface etc.. However, the best vertical gps reading could probably be a yard off. Thats my idea, especially thinking about lakes without official water level outside US.<br><br>Hopefully garmin will let us get the raw data from qucikdraw. Being open with the dàta will allow us to tinker with it and possibly improves it too. Their handheld gps units certainly benefitted a lot from user contributed 'open' data from openstreetmaps.

GPS altitude readings are far less accurate than earth surface 2-D.